Combined stimulation, lesion, and degeneration experiments involving escape responses to nociception in the subthalamic field (of Fore1) have shown that this region carries a significant collateral fiber path from the mesencephalic tegmentum. The related degeneration data strongly suggest that such fibers extend rostrally to the centrum medianum, nucleus parafascicularis, centralis lateralis, paracentralis and also to the nucleus ventralis medialis and ventralis lateralis. Implanted tooth pulp electrode stimulation-lesion studies are indicating that the most probable synapse for such pain fibers which pass through CM and PF is in the nucleus centralis lateralis and paracentralis. "Vicious" cats with ventromedial hypothalamic lesions, followed by secondary lesions in the CM-PF complex, suggest that this nuclear group is in still another way related to nociceptive and/or nonspecific sensory mechanisms.